Ship coatings are used as topcoat on ships' hulls or other underwater structures in order to prevent the colonization and growth of marine organisms, such as barnacles or algae for example, so-called biofouling. In the context of the present invention, underwater structures refer to the bottom or hulls of ships, constituents on and below the waterline of watercraft, solid banks, nets, port facilities, wind turbines, buoys, pipelines, bridges, aquaculture nets, facilities related to submarines, offshore installations such as drilling platforms, pipes, wavebreakers or marine anchors.
This growth or biofouling has historically been a considerable disruptive factor for the marine industry and shipping. The organic growth consists especially of barnacles, mussels, fungi, snails, algae and further microorganisms in which algae are the carrier material for macrofouling.
Like all objects present in seawater, a hull or a ship's propeller can be fouled completely within a few months with so-called biofoulers. The water resistance of a completely fouled hull increases immensely in this case and with it an increase of fuel costs of up to 40%, which result in marked economic and ecological influences. In addition, the controllability may be impaired, which represents an enormous safety risk and also leads to damage to the ship's hull.
To maintain the antifouling of maritime ships today places a series of various requirements on ship coatings. They should on the one hand be cost-effective while on the other hand have the longest possible service life. Additionally, they are dependent on a high and continuous efficacy as far as possible against all potential fouling organisms, a low surface roughness, a high resistance to mechanical and chemical stresses and favourable docking intervals.
The docking intervals of maritime ships are not however defined by fouling of ships' hulls but are determined by the classification societies or by the provisions of ship regulations. The average docking interval of the world's merchant fleet is currently just under 30 months. According to the specification of the classification societies, standard ships are to be taken into dock after an operating period of 2.5 years so that the ship's bottom can be investigated in the context of an intermediate inspection. After a further 2.5 years' operation, the renewal of the class is pending which in turn makes docking unavoidable. Moreover, all passenger ships have to meet ongoing regulations. They have to be annually inspected in the dock. An increasing number of ships are equipped such that the intermediate inspection may also be conducted in floating condition (In Water Survey, IWS). By means of an IWS, one docking per class period (5 years) is eliminated. Since an IWS ship therefore remains in the water for 60 months, this has to be taken into account when choosing the corrosion protection and the antifouling system.
The use of organotin compounds has been forbidden in the EU since 2003, and therefore the most widely used paint up to that point based on tributyl tin (TBT) may no longer be used. In addition, all old stocks of TBT on ships' hulls had to be removed by 2008. TBT had fallen into disrepute, especially owing to its hormone-like property, which had created in whelks, inter alia, in the North Sea for example, a high proportion of sterile individuals. In principle, it is apparent that chemically effective protective paints which are based on the controlled release of biocidal substances such as TBT, copper or organic active ingredients, are increasingly being replaced by novel research approaches. Since the risk of long-term consequences or harm of chemical fouling protection methods in the past could only be assessed with difficulty, nowadays effort is being made to develop ecologically compatible antifouling techniques, so-called “non-toxic” antifoulings.
Due to the EU biocide guideline of 1998, all active ingredients used to date and likewise all new active ingredients appearing must be tested. The aim is to forbid all chemicals which are carcinogenic, which alter genetic material, which impair fertility and also are persistent and accumulate in food chains. Only when there is no alternative are certain biocides approved for a transitional period. Following a positive evaluation, these are then included in Appendix I/IA of the guideline of the EU and may be used. In the case of a negative assessment, the active ingredients are published in a list of non-approved active ingredients and must be taken off the market within 12 months. There are currently ca. 35 substances on the list of active ingredients no longer approved for antifouling, among them formaldehyde, Captan CAS Reg. No. [133-06-2] and the formerly very frequently used Diuron CAS Reg. No. [330-54-1]. The evaluation of other existing substances is currently being conducted.
DE102009014685 A1 describes the use of solvent-free and light-resistant coating materials based on an amino- and/or hydroxyl-group functional reaction partner, which can be crosslinked with isocyanates, which exhibit an antimicrobial effect based on metal ions, especially silver cations.